Physical Attraction

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Physical Attraction The Mysteries of
Magnetism
Joachim Stöhr SSRL/SLAC
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Magnetism and Humans
Animal Magnetism Mesmerizing Magnetic
Healing
Magnetic Attraction
From myth to science ..
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Magnetic Objects
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Magnetic Devices
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Overview of Talk

• A historical perspective the spin on magnetism
  
• Magnetism today the hi-tech society
• A Glimpse of the Futureultra-small, ultra-fast

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A historical perspective

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The term magnetism
Legend Shepherd by the name of Magnés found
that his iron tipped cane was attracted to rocks
More probable Name comes from city of Magnesia
(modern Turkey) surrounded by magnetic rock
deposits
Thales of Miletus (Greek, 634 - 546 BC)
first described magnetism as the attraction of
iron by lodestone - lodestone is the naturally
occurring mineral magnetite Fe3O4
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Si Nan - the south governor
China, ca. 200 BC
magnetic lodestone spoon
south
bronze plate
direction pointers likely used for feng shui
- the method of achieving harmony with the
forces of nature by properly aligning
buildings and placing of objects.
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Earth is magnetic - compass follows its field
Naval navigation China in late 11th or early
12th century compass became known in Europe
sometime later in the 12th century
In 1600 William Gilbert published his book De
Magnete - About the Magnet he explained that
compass needle points north-south because earth
is magnetic
William Gilbert (England, 1544-1603)
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Earth field mostly from electric currents in the
liquid iron outer core
Field changes direction about every 500,000 years
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Around 1800 mythical magnetism
Franz Anton Mesmer theorized that "animal
magnetism" accounted for his ability to heal.
Mesmerizing a patient
Franz Anton Mesmer
(Germany/Austria 1734-1815)
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The mystery of magnetism, explain that to me !
No greater mystery, except love and hate.
Around 1800
magnetism is fundamental, it is just there it
does not need to be explained
Natural Philosophy two opposites make a
whole love hate black white north
south plus minus
Johann Wolfgang von Goethe
(Germany, 1749-1832)
contains important modern element there are
no magnetic monopoles!
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1819 a breakthrough discovery
Hans Christian Oersted
(Denmark, 1777-1851)
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1831 The foundation of the industrial society
Electric generator motion
electricity
Electric motor electricity
motion
Michael Faraday
(England, 1791 1867)
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Electricity is big
US electricity retail sales 250
billion/year ( 0.25 trillion)
Total Gross Domestic Product (trillions of ) 1.
United States 10.9 2. Japan
4.3 3. Germany
2.4 4. United Kingdom 1.8 5. France
1.7 6. Italy
1.5 7. China 1.4
Hydro-electric - water drives turbine
Nuclear - heats water - steam - turbine
Fuel - burns - hot gases - turbine
About half of the US energy is consumed as
electricity
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1845 Magnetism and light a connection !
again Michael Faraday
1791 - 1867
Light must have a magnetic component
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1864 Maxwells equations coupling of electric
and magnetic phenomena
Light is an electromagnetic wave
James Clerk Maxwell
Ludwig Boltzmann (Germany,1844-1906) Was it a
god who wrote these symbols unveiling the forces
of nature?
(Scotland, 1831 1879)
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only wavelength is different
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The electro-magnetic spectrum wireless waves
at the speed of light
Visible light
It is hard to imagine our society without
wireless technology !
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1921-1928 Getting to the origin of magnetism
7 years that changed physics and magnetism

• The concept of the spin (Pauli, Uhlenbeck
  Goudsmit, Dirac)
• Quantum theory (Heisenberg, Schrödinger, Dirac)
• Magnetic exchange interaction in materials
  (Heisenberg)

The mystery of spin when measured, it is always
along a quantization axis up or down
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The inside of magnets origin of magnetism
magnet arrangement of atoms with aligned spins
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Magnetism today the high-tech society
beyond electricity and wireless
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The spin on electronics magnetic devices in
computers
chip - RAM
disk
0 and 1 bits small magnetic areas with
opposite magnetization direction
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Magnetic recording technology
Courtesy of Jan Thiele, Hitachi
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The Data Storage Industry 53
billion/year worldwide revenues
IBM RAMAC 1956
1 song
stack of 50 giant discs, 24" diameter
total 4.4 MB - 35,000/year rent
Today
200 GB 200, 000 MB - 90
10,000 songs
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Magnetic recording Small and fast !
1 mile/hour
1000 miles/hour
Incredibly small bits incredible writing and
reading speeds
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The invisible ultra-small world
understand size limits -- no
stable bits--
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X-ray images then and now
X-rays have come a long way
0
1
bits
10,000 times smaller
1895 W. Röntgen, Würzburg
1993 SSRL/SLAC
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A Glimpse of the Future
exploring ultrafast time scales .is there
a data storage speed limit ?
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Present switching pulses are generated by current
flow through wires
Oersted fields
most advanced technology 100 picosecond (10
billionth of a second) current pulses magnetic
recording works fine
With this method we cannot explore faster
switching today . is there a
speed limit ????
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The ultra-fast world
How can we explore this void?
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An electro-magnetic brainstorm
Create an artificial lightning bolt and use
it to switch a magnetic sample !
(Prof. ETH Zürich, Switzerland)
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Creation of large, ultrafast magnetic fields
Conventional method - too slow
Artificial lightning bolt an electron
accelerator
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Magnetic writing with SLAC beam
sample
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The Speed Limit of Magnetic Switching
tpulse 3 ps
tpulse 100 fs
0
1
0
1

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90 mm
90 mm
30 times faster than conventional -- switching
still works reliably --
1000 times faster than conventional --
switching is not reliable --
.. but we dont understand why!
There is a speed limit!
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The magnetic recording limits size and speed
size
speed
factor lt 1000 to go
factor 30 x 150 5000 to go
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The future seeing the invisible at ultrafast
speeds
Linac Coherent Light Source LCLS the first
x-ray laser in the world
Far Hall
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In Summary..

• Magnetism .
• is an old phenomenon and topic
• has many important practical applications
• navigation electricity wireless
  communication medical imaging
• underlies modern data storage technology
• may be used in future for computer memory
  and quantum computing
• remains an exciting research topic

... the mystery of magnetism continues...
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Acknowledgements
Ann Mueller, SSRL Science website http//www.ho
wstuffworks.com My research group http//www-ss
rl.slac.stanford.edu/stohr http//www-ssrl.slac.s
tanford.edu/stohrgroup